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Патент USA US2105016

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Jan. 11, 1938.
Filed Jan. 2, 1936
4'Sheets-Sheet l
. 43:4.
Jan. 11, 1938.
Filed Jan. 2, 1936
4 Sheets-Sheet 2
Jan. 11, 1938. ‘
Filed Jaxi. 2, 1936
4 Sheets-Sheet}
Jan. 11, 1938.
|-|_ H, sMrrH
Filed Jan. 2, 1956'
4 Sheets-Sheet 4
Patented-Jan. '11, 1938 .4
’ ’: '
mass“ rizwsslzssron'sys'rair
Howard'H. Smith, Chicago, 11]., 388131101‘ to As
sociated Electric laboratories, Inor, Chicago,
11L,~ a corporation of Delaware
- Application
2, 1936, Serial No. 57,116
vi ‘Claims.
,(01. meals)
, _The present invention relates to telephone
‘transmission systems, but is concerned more par
same time period by arranging thatthe times
of reproduction and retransmission of the high
ticularly with multiéchannel telephone transmis- ' frequency currents resulting from the four con
sion systems.
versational records be interspersed. At the dis
The object of the invention is. the- production tant end of the circuit, the incoming higlr fre- 5
7 ' of a new and improved system‘for providing for
quency voice currents are recorded intermittently
I mulgi-‘channel telephone transmissionf
as concerns any individual conversation, and are
reproduced at the original recording rate, where- , v
by the reproduction of the received and recorded
currents'is continuous, and at the original rate. 10
The‘systemv disclosed herein, like previous ‘sys
tems} for providing multi-channel operation over
-By making the time units involved su?lciently '
the Some common‘ circuit path, is‘based vonthe
fact ‘that -a,telephone'-ci_rcuit may serve as a;
transmission medium for'a frequency band many
i ‘15
short, the 'delay occasioned by the recording and
reproduction may be reduced su?icie'ntly that the
persons conversing are not aware that the trans
times wider than the frequency‘band-necessary
mission is not proceeding uninterruptedly.
I 15
With the novel-arrangement just outlined, the _
found_ that if a band-of voice frequencies 3000 time elapsing during 'the transmission of teley
cycles‘wide, extending from about 200v cycles to 0 phone conversations is divided into small unit.
about 3200*cycles is transmitteduniformly?to intervals, and each unit interval is further sub
vfor ordinary telephone conversation. It has been
the exclusion of another frequencies which may
v20 be‘
contained in the. voice of a speaker, a com-7
divided into four sub-intervals, each sub-interval
being. allotted to one of the conversing subscrib
mercial quality of - intelligibility results.
Now,. ers. This allot'ting, together with the recording‘ an inter-exchange or inter-city telephone cir 3and
transmitting over the common- line is ac
. cuit is ordinarily capable of transmitting or car
.25‘rying ffrequencies satisfactorily up to‘ 30,000, complished by what may be termed a distributor.
cycles} or higher. It is obvious, therefore, that, This distributor allots regularly recurring'inter- 35- '
as c
a suitable transmission system can be devised, I vals of time to each of the four incoming chan
several conversational channels may be secured‘ nels, while a receiving distributor at the distant
end of the line makes a similar allotment of the
by arranging that the extended frequency-trans
mitting characteristics of the telephone circuit be sub-intervals of receiving time.
- It has been chosen to illustrate the invention
. The‘ novel system disclosed herein is based on a as applied in obtaining four-channel, two-way
the principle of multiplying all of the necessary
telephone transmission over an inter-city tele
‘ ; frequencies of a telephone conversation‘ by a sui
35 ?ciently la'rge common factor that the’resulting
transmission frequencies compose a band of a
l '
width commensurate'with the frequency-carry-
Description of drawings
~'lftefe'rrin'g now to the accompanying drawings,
Fig. 1 showsan end view of the mechanical con
may be ?ve, for example, if the chosen upper struction of a combined transmitting and receiv
frequency limit of the circuit is‘ slightly ‘invexcess ing distributor designated generally as the ‘dis
~_of 16,000 cycles, and if 3200 cycles is. chosen as - ‘ 'tributor DI, Fig. 2 is a side view of the receiving
the upper limit of voiceinput. 'I'hisfr'equency ' distributor DI, Fig. 3 is a circuit drawing show
multiplication is obtained by ?rst recording a ing the distributor DI used ‘asthe transmitting
and receiving distributor atone end of the tele
small portion of a-train of voice currents; re
45 producing these recorded voice currents at a rate phone line TL, at the other end of which the-dls- >45
which is ?ve times as' fast as they'were’recorded; tributor ‘D2 shown in Fig. 4 operates to receive‘
and sending the reproduced high-frequency cur ' ‘from the transmitting portion of the distributor
ing' capacity of the circuit. This common factor
1'IFhereeording may‘ take place continuously,
so while the’reproducing‘ and transmission over the
line/ takes place intermittently,
?fth the line time. Allowing-for inter~channeli
switching time intervals, it has been found that
under- the assumption above made four conver
j‘ sations'inay be sent over the line duringvthe.
DI and to transmit ‘to the receiving portion of ‘the
distributor m.
a v
Dm'ArLm Drscalr'non
The invention havingbeen described generally,
a detailed description will be given, for which purpose the mechanical construction of distrib- '
utor DI will ?rstbe described
7 ~
steel, for example. Magnet 42 of channel B may
The distributor D1
The distributdr DI consists of certain parts
be likewise leaving a voice-current record on the
portion of' the disc passing by its pole faces, as
mounted on|the base i. It comprises essentially
a central shaft 2, journaled to rotate within a '
'hollow- shaft 3, which in turn is journaled to
track of disc i8 thatv has just passedthe magnet
42 of channel B, this portion continues to be
rotate within the sleeve I3,supported by the
housing I2.
are magnets 43 and M of channels C and D.
Considering now a portion of the outer sound
The shafts 2v and 3 are arranged to ' rotated and a magnetic sound impression is left
on the disc, which impression or record is ex—'
be rotatedlin opposite directions and at different
speeds by the motor 4, on whose shaft 5 the
a reducing geaér 'i-which is rigidly secured to the
tended until the portion in question starts to
approach the group of magnets containing mag
net 4I. When magnet 34 of this group is reached,
central shaft
the record is completely removed from the sound
-10 gears 6 and 8 are mounted.
The gear 6 drives
The motor 4 'is' assumed to be
rotatable at a constant speed in a clockwise direc
tion as viewed from ‘the left, whereby the central
15 shaft 2 ‘rotates in a counterclockwise direction.
The gearea, rotating in a clockwise direction
because it is secured to shaft 5 of the motor,
drives the reverse gear 9 in a counter-clockwise
direction, whereby the auxiliary gear Ill is driven
20 in the same ‘direction. The gear I0 drives the
reducing gear II in a. clockwise direction. Since
the gear I I is secured rigidly to the hollow shaft
3, the shaft 3 is rotated in a clockwise direction,
but at a much lower rate than the rotation of
25 the central shaft 2 ma counter-clockwise di
track because the portion of the track under the
magnet 3tv is saturated by the strong magnetic
flux emanating from the poles of magnet ,34.
As the portion of the sound track travels still
further, magnet 35, which is less strongly mag
netized than magnet 34, and in the reverse direc
tion, removes the effect of the saturation of the
sound track and restores the portion to a normal
non-magnetized state. Therefore, when the por
tion of the disc in question progresses'further
and passes underthe recording magnet M of
channeLA, all evidence of the previous sound
‘record has been removed and the portion of the
disc is in a ‘receptive condition for the impres
The track wlieel I4 is secured to the hollow sion of a further magnetic sound record. ,
shaft 3,,at the left end of the shaft, and the brush
What has been described is, of course, a con
wheel I5 issecured to the left end of the central tinuous process, as the disc wheel I4 is in con 30
shaft 2, whereby the wheels I4 and I5 are rotated tinuous -motion and, is therefore continuously
respectively by the shafts 3_ and 2, the wheel I 4 moving the track disc I8. As a result, the por
' revolving relatively slowly in a clockwise direc
tion of the disc between a recording magnet, such
tion while the brush wheel I5 revolves at a rela
as 42, and the next succeeding erasing magnet,
tively rapid rate in a counter-clockwise direction.
The track wheel I4 has the track disc
such as 34', contains a. portion vof a. spoken mes- f.
sage the length of which depends upon the
clamped between its rim and the disc clamp I9 amount of time required for the disc 'to travel‘
to provide two sound tracks on the disc I18," an _ from the recording magnet to the next succeed
outer track for temporarily recording telephone
conversations to be transmitted over a. multi
. channel line, and an inner track for temporarily
recording conversations received over the multi
channel line before they are placed on local
single-channel lines. The ‘two sound tracks on
disc I8,>_‘carried by the track wheel I4, are
45 separated by the stiffening rings 20 and 2I which
are provided to render the relatively thin track
disc l8 su?iciently still‘ that it is not distorted
materially by the pull of the erasing electromag
ing erasing magnet. Therefore, in order that
none of the recorded speech be1lost,_it is essen
tial that a. reproduction be made of what is re
corded once during each successive time interval
of a length no longer thanv the, length of time
required for a portionof the discto travel from
. a recording magnet such‘ as 42 until it comes
under. the in?uence of the next succeeding erasing
magnet such as 34.
The _ reproduction and transmission of‘ th
recordedv voice currents is accomplished by the‘
'50 disc is made thin enough that a sound record , transmitting reproducing magnet'28, which is
mounted on the .rim of the brush wheel I5 near
nets which are‘hereinafter described. , The track '
magnetically impressed on one side may be re
its periphery and counterbalanced bythe weight
produced by passing a pickup coil along the othervv 30, mounted at a point wdiametrically opposite the
As thel disc I8 is revolved in a counter-clock
5.5 wise direction, and considering now the outer or
horseshoe electromagnet 28. The reproducing,
transmitting, magnetv 28 is maintained incon
stant connection with the transmitting circuit .~
transmitting sound track (lying outside the stiif
ening rings 20 and 2|) ‘the disc at any instant
'through the medium of vthe slip rings 25 and
the stationary contact brushes 2!, while? the 'r'e- *
may be considered asv'divided into quadrants by
ceiving, recording magnet 29, mounted near 1the.
60 the four groups of electromagnets mounted on, inner edge "of therim' of the, brush wheel I5 is‘
the stationary sending ring “5.. Each of these
similarly maintained in connection with the re
groups of magnets corresponds to ‘a, separate, tele-' ' ceivingjc‘ircuit through the rings 21 and the/sta
phone transmitting channel "as is indicated ‘in. , tionary contact’ brushes 26. The weight 3| is
7 Figs. 3 and 4, wherein the channels have been _ mounted" so as to counter-balance the electro
'65 designated as A, B, C, and D, respectively. Mag
net _4.I ‘is one of the‘ three horseshoe electromag
nets of channel A; magnet 42 is one of- the three
magnets'of channel B; magnet 43 is one of the
magnetv Z9.’ ‘ '_
.Since the
distributor DI is a combined trans-l
mitting distributor and receiving distributor, it is
providedfwith receiving, reproducing stationary
three magnets'of ‘channel/C; and magnet“ is; magnets in addition'to. the transmitting, record
70 one of the three‘ magnets of channelD. Voice, ing st‘ationary‘magnets. These receiving,'record
currents passing through the coil '4I asthe disc» ing magnets for channels A, B,_C, and’ D are re
I8 .is rotated in a clockwise-direction leave a‘magn ~ spectively ‘II, ‘I2, 13, and 1-4, all of which are
netic voicevrecord ‘on the outer sound track of
shown in Figs. 3 and 4, in-addition to being shown
magnetic material of relatively highretentivity;
the adjustable stationary receiving ring I'I, whose 75
disc I8, as the disc- I8 is assumed to be made of’ - in Figsil and 2. These magnets are mounted on
- ,adjustable feature is provided for a purpose
which will be made clear in a subsequent part of
the description.
the transmitting branch to,the recording mag
net 4|. The reason for this arrangement be-'
comes apparent when it is pointed out that other- _
Adjustment of the receiving
ring I‘! is provided by'turning the worm 22 in the wise voice currents received from the reproduc
desired direction, such as by inserting a screw ing magnet ‘ll would be transmitted to the re
driver or similar instrument lathe-slotted end ' cording magnet 4| and sent back over the cir
of the shaft which supports the worm‘ 22. The cuit in the opposite direction, which would tend
worm 22 cooperates with the worm'gear cut on to produce undesirable “singing”. The balance
the ‘periphery of receiving“ ring II, which ring is coil 65 and the arti?cial line 66 are provided in
10 rotatably mounted on a. portion ofthe bearing
association with the jack J2 for the same pur
‘ ,sleeve i3. The group of magnets carried by the
receiving ring" may thereby be adjusted with
the distributor DI, it is to be observed that
respect to the groups of magnets carried by the ‘theAtwindings
of the erasing electromagnets, such
transmitting ring l'6. )
' T
A further feature of adjustment of the dis
tributor is, provided by the worm 23 and the as-“
sociated worm gear secured around the housing
of the driving motor 4. The motor 4 is mounted
in brackets 32 and 33 so that it can be rotated
bodily when the worm 23 is turned in the desired
direction, which turning is facilitated by the slot
in the end of the supporting shaft. The desira
bility of this adjustment will be made apparent
the exchange battery ?ows through this series
circuit under the control of the regulating rheo
stat 46 to magnetize the erasing magnets su?i
ciently to bring the portion of the sound track
under the in?uence of the respective magnets to 20
the saturation point in order to remove previous
ly made voice records. Since disc I8 is rotated
in a clockwise direction,‘the saturated parts of
- the disc then come under the in?uence of the
The system
restoring magnets such as 35. These restoring 25
Referring now particularly to Figs. 3 and 4, it
is to be noted that the telephone line TL extends
between exchange 1 and exchange 2.‘ These ex
magnetsare connected in series with .each other
and are supplied with current from the exchange
battery byway of, the regulating rheostat 45.
30 changes are assumed to be' located in di?’erent
As is evident from the fact that the connections
are made‘in reverse direction to the restoring 30
magnets, the magnetic ?ux emanating from the
restoring magnets is in the oppositei'direction
cities,‘ whereby the interconnecting lin'e TL is
sui?ciently valuable because of its length that it
.is economical to supply additional terminal
,equipment in order to provide the additional tele
35 phone channels. A manual switchboard is as
sumed to be provided in each of the exchanges.
The ‘jack J l is one of the jacks atlthe manual
to that emanating from the saturating erasing
switchboard of exchange 1, while thejack J2 is
' _ one of the jacks at the manual switchboard of.
‘exchange 2.
as erasing magnet 34 associated with channel A,
are all connected in series, and that current from 15
These/two Jack's, as will be‘ more
40 fully'pointed out hereinafter serve as the termi
magnets. The result of this is thatthe portion
ofthe disc passing under a magnet such-as 35 35
would be demagnetized and then saturated in
the opposite direction’ if the restoring magnets \_
were of the same strength as the erasing mag
nets. However, the restoring magnets are of
lesser strength than the. erasing magnets, for
male of one of the channels (channel A) which
vwhich reason the previously e?ected saturation
is undone only to the extent that the portion
equipment LEI is associated with’ the lack Jl. of the sound track coming from under the in
- This- line equipment may be any standard equip
?uence‘ of a restoring magnet such as 35 has
45 ment such as is used with carrier-current tele- . little or no magnetism. This condition may be
phone systems, and it is arranged togclose a light
regulated somewhat by an adjustment of the.
_ is providedover'the common line TL;
The line
ing circuit for the lamp Ll when the operator at
exchange 4 is to be signalled from exchange 2,
- which signalling is carried on by signalling cm‘
50 rent in the range. of voice frequencies, as is well
known. The line equipment LE2 and the lamp
L2 are associated with the. jack J2 in the second
rheostat 46.
Considering the receiving portion~of the dis
tributor DI, the erasing magnets'such as .36 are
connected in ‘a series circuit controlled by‘ the 50
rheostat 41, while the restoring magnets such as
31 are connected -in a' series circuit controlled by
exchange to perform similar functions. vEach the rheostat 48.
of the three other two-.way channels provided‘ ,As previously pointed out, the magnet 28 is the
over the trunk' line TL may be. similarly travelling reproducing transmitting magnet, be 55
equipped, although the jacks and associated line ' ing mounted on the brush wheel |5,.Fig. 1, so that
equipment of these'other channels have been ‘it moves relatively rapidly in a_counter-clockomitted for the sake of simplicity.
The balance coil 55 is introduced between the
- wise direction, while the magnet 29 is ‘the travel
ling receiving recording magnet, also'moving in
60 line equipment LEI ‘and the ‘distributor DI. This ' a counter-clockwise direction. The ampli?er 51
balance coil, along with thearti?cial line 56 op
is the outgoing line ampli?er used to amplify the‘
erates in the well-known way to provide separate‘ high-frequency outgoing voice .currents before
. voice channels outgoingirom and incoming to ‘ they reach the common line TL.
the jack Jl, The outgoing channel extends from
The arti?cial ‘
line AL is provided tobalancethe character
istics of the trunk line TL, whergbythe balance
the mid-points of the line windings oi'the bal
ance-coiljto the recording magnet 4|, while the , coil ,5. may serve ‘to prevent outgoing voice cur
incoming channel extends fronithe reproducing’
rents'i'rom reaching the-incoming branch asso
byway of the manual switchboard. voice currents
through the incoming line ampli?er. “,which
\-_ magnet TI to the lower winding of coil 55. When ' ciated with-the ampli?erj?, as discussed in con
'- 7o the arti?cial. line, 56- is properly ‘balanced to nection with the balance coil 55. The incoming ‘
match the local line connected‘ with the jack J I ~ voice currents; ‘on the other hand, are transmitted 70
- received from the reproducing magnet 'llyare 're-'
' peated-alike to the arti?cial line "and the local
‘line, and no- voice currents are driven through
leads into the common ‘receiving recording mag
net 23 by way. of brushes ,2‘ and slip-ring 21. ‘In '
'exchange'2, theline TL ‘is provided with ‘balance
coil ll, arti?cial lineill, input ampli?er "I, and
output ampli?er ‘19, corresponding respectively,
to the parts 58, 59, 51, and 60 in exchange 1.
so that the associated channel may be used by any
one of the number of operators. Assuming that a.
The distributor D2 may be like the distributor
'DI; the transmitting and receiving magnets 38,
39 correspond to the magnet 28, 29 of the dis
tributor Di; the stationary recording magnets
6! to 64 correspond respectively to the recording
‘magnets 4| to 44 of the distributor 'Di; and the
stationary reproducing magnets 5| to ,54 asso
10 ciated with the receiving portion of the dis
tributor D2, correspond respectively to the sta
tionary reproducing magnets ‘H to 14 of the
receiving portion of the distributor DI.
call is received at exchange 1 and is to be com
pleted through exchange 2, the operator at ex
change 1"who receives the call may makethe
usual tip busy test on the sleeves of the jacks such
as J]. ‘Assuming that the jack J i tests idle, the
operator may insert the plug (notv shown) of her
cordcircuit into the jack J i, causing this chan
nel thereby to. test busy at the other test positions.
The operator may now project ringing current
over the channel A through the jack J i . I It is'as
Operation of the system
bols associated with the jack J i, this jack may be I
multipled with other positions of the switchboard
sumed that the line equipment LEi contains
equipment similar to the so-called composite
ringing equipment for responding to‘ringing cur
rent by“ relaying current at a selected frequency
within the voice, range for‘ signalling purposes»
This relayed‘ current traverses the ' channel-.A
portion of the distributor Di and passes over the
trunk line TL ‘and is repeated through the chan
'nel-A- receiving portion of the distributor Di to
the line equipment LE2 vassociated with the'jack
For the successful and satisfactory operation
of the system; it is. necessary that the syn
chronous motor 4 of the distributor DI drive its
shaft 5 in synchronism with the corresponding
20 shaft oflthe distributor D2. This result may be
obtained, for example, by driving the motors
from the same system of alternating-current
power distribution, or the driving system may
depend largely upon local power‘with a speed
25 correction obtained over an interconnecting line . J2. The°line equipment LE2 ‘is ‘assumed to have
as is done for instance'in‘ multiplex telegraphy responding-equipment therein which responds to
or in systems for maintaining synchronism in the the relayed ringing signal by lighting the line
transmission of still pictures by wire._ When the
system {is tobe started into operation, the mo
tors of the distributors at the two’ exchanges; are
started and are caused to run in synchronism.
Phasing the distributors
In‘ order that the system operate‘ as intended,
35 it is further necessary to bring each receiving
distributor into phase with the transmitting diss
tributor from which it receives. For this purpose,
lamp L2 as a .call signal to the operator. ' The op
erator in exchange 2 may now respond to thissigl
nal by inserting the plug of an idle cord circuit '
‘into the jack’JZ to extend the connection. ‘
Ring-01f and other supervision may be con
trolled by relayed signal currents lying within
the voice-frequency range,‘ as pointed out in con
nection with they original signaling operation 35'
above described. '
__ I
‘ 7
Transmission of voice currents
a source of tone current may be connected to,
It may be assumed now that separate inter-ex
the tip and ring conductor of the jack J i‘, while
change connections exist by way of the four chan 40
40 the person in charge of the equipment at ex
change 2 connects a receiver to the jack J2 and nels, A, B, C,'and D, of the line TL, under which ‘ '
listens for the tone which is appliedthrough the ' condition the maximum use may be made ofthe
trunk line ‘TL. A description will now begiven‘ ,
of theoperations that‘ take place during one or _ '
DI) is then adjusted by the worm and ‘gear ar- ' more cycles of operation of the distributor. . It
rangement previously described, until the tone may be assumed that each of the four subscriber's .
applied at the jack J l is heard at the jack J2 in exchange 1 is talking at the moment the‘de- .
-jack J I. The receiving ring of the distributor
D2 (corresponding to ring I‘! of the distributor
scription covers. Under this condition, voice‘cur
as a continuous uninterrupted tone. This ad
' justment may be veri?ed by associating the test - rents are being received‘continuously at each of
the recording magnets M, 42, 43, and 44 of the corresponding to channels B, C, and D. When transmitting portion of the distributor Di ;_: the
the adjustment is correct, none of the 'tone ap - outer‘sound- track of the track disc i8 is being
plied to‘ jack Jl can be heard at any other one driven continuously in a ‘clockwise direction under " _
50 receiver with the other three jacks (not shown)
Th‘ereceiving portion of the distributor Div
may be brought into phase with the transmit
ting portion of the distributor D2 by a similar
method. For this purpose, the tone source may
be connected to the talking conductors‘at the
60 jack J2, and areceiver may be connected to the
direction or the other until the worm gear cut on
reproduced clearly. At the same time, the trans
mitting reproducing magnet 28 of the distributor
DI .is being driven in a counter-clockwise direc
tion at an angular velocity', about‘ ?ve times that
of the track
l8, whereby the magnet 28 makes
‘one complete revolution in the time‘requireddor
the'periphery of the-receiving ring I'I drives the
ring into the correct position,- in which\position
65 the tone applied at the jack J2 will be heard at
far enough to reach the in?uence of the next suc
ceeding erasing magnet suchv as 34. Considering
jack J i .
The worm 22 is then turned in one
the jack J I as a continuous tone and will not be
heard at all at any one of the‘ other three jacks
associated with the ‘system and corresponding
respectively to channels B, C, and D. When this
70 has been accomplished, ‘the four two-way chan
nels over the inter-exchange trunk line TL are
available for service.
' -
As is indicated
by the
up commoneconnection
the pole pieces of the magnets II to M at a rate .
which is su?icient to elongate the recorded mag 55
netization curves su?iciently. that they may be
a‘portion of the disc l8 to pass ‘from under the
poles of a recording magnet‘such as 42 and travel 4
now channel B in particular, and at a time when. '
the reproducing transmitting magnet 28 is pass‘
ing over the pole pieces of the recording magnet 5
42, the portion of the outer sound track of the 70
disc l8. which is'at that moment under the pole
pieces of magnet" travels _until it is about to
come_under the in?uence of the erasing magnet
‘ 34. At this point, the‘magnet 28, which in the.
meantime has rotated around over channels C,‘
D, and A, comes from the ?eld of in?uence of the
magnet 34 in time to resume the reproduction and
over the C channel to the subscriber in exchange
2, magnet 39 travels over the other three quad
rants. It comes again into effective relationship
transmission of-’the record produced by magnet
42 before an unreproduced- portion of the message to quadrant 0 just as the last of the previously
-5 .is erased. The next portion, therefore, of the recorded portion of‘ the message‘ is reproduced. 5
message being received over channel B from the
In this way,’ a continuous reproduction and
transmission to channel C branch in exchange 2
mitted over the line by the reproducing‘ and trans- . isaccomplished. A similar result is accomplished
mitting action of the travelling magnet 28 and at in ’the same way for each 'of the other three
local subscriber in exchange .1 vis quickly trans
10 a rate which is about ?ve times the recording rate.
This action occurs on each revolution of the trav
elling magnet 28, and it occurs for each of the
four channels.
It is to be noted that about one-?fth of the line
time is unused in the embodiment illustrated ow
ing to the necessary space occupied by the mag
,net groups such as 34, 35, 4|‘. This time may be
reduced of course, by making the magnets small
er “or preferably by enlarging the radius of the.
20 brush wheel 28 and of the magnet rings l8 and I1,
along with the radius of the track disc l8. It is to
be observed further that, although a considerable
disturbance may be created when the traveling
magnet 28 passes over ‘an erasing magnet such_
as 35, the current resulting from this disturbance
reaches the distant receiving magnet 39 at a time
when this magnet also is passing over an erasing
magnet, for which reason thevdisturbance is not
recorded at the distant end and does not there
30 »fore appear 'in the conversation heard by the
distant subscriber in association‘ with whose chan
nel the disturbance may be created.
Reception of voice currents
Considering now the way in which the high
frequency interspersed message groups are sorted ’
out and reassembled into separate, continuous
,messages at the distant exchange, it will bere
called that the distant receiving recording mag
40 net 39 'is'being rotated in 'synchronism with the
reproducing transmitting magnet 28 and in phase
with it except for the small time-interval dis—
placement representing the transmission time of
the voice currents over the line TL from exchange
45 1 tonexchange2. Consider now the sub-interval
‘of time which begins when the transmitting re
producing magnet 28 of the distributor DI is leav
ing the in?uence of erasing ‘magnet 86 'in the
channel~B group. When the surge of current
50 tran'smitted'as a result of magnet28 passing over
this erasing magnet reaches the distant exchange,
Two-way operation
While the transmission overv the four channels
from exchange I to exchange 2 has been taking
place as'above described, the transmitting por
tion of distributor D2 has been‘ cooperating with 15
the receiving portion of the distributor DI to
effect a similar four-channel transmission in ‘the
reverse direction in the event that any voice cur
rents are generated on the respective channels in
exchange 2. It will be understood of course that, 20
if the subscribers in exchange 1 cease talking and
the subscribers in exchange 2 all start talking, the
four-channel operation proceeds in the-reverse
direction in the manner described. However, it
makes no di?erence'to the operation of ‘the dis 25
tributor system whether ornot voice currents are
travelling in the same direction over all the chan
nels or even whether or not they are travelling in
only one direction over one channel at a time or 30
not. Voice currents may be transmitted simulé
taneously in both directions over each of the‘
channels A to D if all‘ of the subscribers should be
talking at once, which discussion is largely of
academic interest except as it concerns the oper 35
ation which takes place when a listening sub
scriber desires to interrupt the conversation of '
the other, possibly to interject a question. In
short, the subscribers interconnected by way "of,
the disclosed transmission system may converse
as they would over any ordinary telephone con 40
nection with the one exception,‘ that there is a
variable delay ot a small fraction of a second
under certain conditions occasioned by the ‘amount
of time required for a recorded portion of a mes
, sage to be sent through the transmitter and re
corded and repeated at the receiving distributor.
Stopping and restarting
In thev event that the system'is to be stopped,
which may logically occur during a period of light 50,
magnet 39 is passing over the erasing magnet 8| ' tra?ic, the power supply of the driving motors
maybe disconnected. When the system is to vbe.
in the channelec group of magnets. , When mag
, net 28 proceeds a little further and has left the restarted the two distributors may be brought into
phase by rotating the frame structure‘ of either of 55
55 in?uence of the above-mentioned erasing mag
the driving moto'rs.' For example, by turning the
. .net, magnet 39 is passing over the pole pieces of
the-‘stationary reproducing: magnet 53 of receiving worm 23 slowly the frame of the motor I is ro
channel C in the distant exchange.
Then, ‘ as
ltated in the proper direction to bring‘the cen
magnet 28 progresses further toward the channel tralshaf/t' 2 andthe hollow shaift'3 into the same
60 C magnet 43 it transmits thelrecord‘ of the voice phase relationship with. respect to the correspond
currents that have been received over the channel ' ing shaftso'n distributor D2 as existed during the
previous operation; When,’ the two‘ distributors
have been brought, into the same phase relation
tacted the channel-C portion ~of the record. __ At that previously existed, the receiving and trans
65 the-‘same timerreceiving recording magnet 39 of . mitting-portions of .allthe channels in birth direc
. C ‘circuit in exchange 1 during- the time interval
which haselapsed since magnet 28 previously‘ ‘con
the distributor D2 isproceeding'tqward the chan- >
nel ‘D magnet group. including magnet SI. . Just -‘
'asrnagnet 28 arrives 'over the pole pieces of the
channel D stationary‘magnet 43, magnet 390!
to .the distributor D2'comes under the in?uence of "
_ lthe restoring. magnet in; the group containing
'_magnet 54. Then, while tlieportion- ofthe track‘
on which a recordihas
'1 the receiving recording magnet 29 ‘during. its
travel in the C quadrant is reproduced and sent
tions willfbé in phase, 'andfindividual adjustments
at the‘ tw'o'di'stributors may be done away with.
This operation will be understood when it is re
called that a synchronous motor
speed ofits rotating‘ shaft‘ constant with respect 70
,to'the frame structure of 'the'motor; ,- Therefore,
if the frame-structure of thev motor is turned so
slowly as- not'to impose an'overload on-the motor,
"the speed 0! “the motor shaft is increased or de
shaft running at- a constant speed with respect to
they were recorded, means for recording a plu- ,
the frame of the motor, as the-motor frame is
rality of received conversations at the same time
- turned in one direction or the other ‘in order to
on the receiving track of each disc as received
bring the rotating parts of the distributor into
over said trunk line, and means for reproducing
the conversations recordedon the receiving track,
whereby a plurality of two-way conversations
the previously existing phase relationship.’
The separate adjustments of the distributor
may be made use of also in order to bring the dis- 1 may be carried on over said trunk line without
tributors into the proper phase relationship with
the magnet groups of the receiving ring of each
=2. In a multiplex telephone transmission sys
tem, a two-conductor trunk line, a distributor at‘ 10
10 distributor suf?ciently displaced with respect to
the magnet of the associated transmitting ring so each end thereof, a plurality of telephone sta
as to minimize any tendency for direct inter» tions connected with each distributor, each dis
tributor including a rotating disc having a trans
group aerial magnetic inteference. ' '
mitting and a receiving track thereon, each sta
Modi?ed arrangements
tion having a magnet for recording outgoing 15
The system herein disclosed may obviously be voice currents on the transmitting track of'its
re?ned in certain respects. For example, the distributor, and a magnet for reproducing re
ampli?ers 51 and 61 may be made to include a corded ‘voice currents from the receiving track,
band pass ?lter which will eliminate from the another element rotating at a greater speed than
'20 reproduced conversation all frequencies which. said disc, said element carrying a transmitting 20
_ exceed a set, maximum, whereby the main'mum' . device which transmits outgoing voice currents
‘frequency transmitted ‘over the line 'I-‘L from the recorded on the disc by the magnets of all sta- ''
distributor DI is limited. This arrangement may
be employed to prevent excessive cross-talk inter
action between adiacent lines similarly equipped,
in which case the ampli?er Bl issimilarly-prm
vided with an inputband pass ?lter to limit~
the frequency of the currents impressed on the
line TL at exchange 2.
Av modi?cation which at once suggests itself
may include the use of a four-wire circuit be
tween the two distributors to replace the line TL,
transmission in on'e'direction proceeding over
one pair of wires and transmission in the other,
35 direction proceeding overthe other pair. of wires.
This arrangement may be used to advantage if
the line TL is sufficiently long that a great num
ber of repeaters are required, in which case sep
arate balancing networks at the various repeaters
tions, and a receiving device which records in
coming voice currents on the receiving track of
the disc for reproduction by all the reproducing 25
.3. In a multiplex telephone system, a plurality
of telephone lines, a trunk line, a distributor for
‘recording and retransmitting incoming and out
going conversation from the lines over the trunk 30
liner and fromv the trunk line to all the lines si—
multaneously, said distributor-comprising a ro
tating disc adapted to receive and retain mag
netic impressions of voice currents received from
and transmitted to the trunk line, a magnet for 35
each line for-recording on the disc and a magnet
for each line-for reproducing from the disc, said
magnets regularly spaced around the periphery
of the disc, and a pair of magnets for the trunk
40 are done away with and simple one-way ampli— rotated relative to the disc for reproducing re; 40
corded data from the disc and transmitting it
?ers may be‘ used, as ‘is well known.
It will be understood that the switchboards in - ‘over the trunk and for recording data on the
disc received‘ over the trunk line.
the two exchangesmay be automatic switch
4. In -a multiplex telephone system, a plurality
boards instead of manual switchboards, in which ‘
of lines and a trunk line, a distributor for dis 45
45 case dial impulses may be transmitted over the
tributing simultaneous voice currents from the
quency' dialling, such as. the system disclosed‘ lines over the trunk line successively, and for dis‘
vchannels by‘ any known method’ of voice-fre
in ‘the application ofvJohn Wicks, Serial Number
tributing received voice currents over the trunk
‘751,802, ?led November 7, 1934.
line .to the lines, said distributor comprising a
rotating disc having one, sound track around its 50
periphery on which voice currents from all the
What is claimed is: Y
1. In a, multiplex telephone transmission sys
tem, a two conductor ‘trunk line extending be
tween two stations, a distributor at each end of
said trunk line, ‘each distributor including a ro
v55 tating disc having a transmitting anda receiv
. ing track thereon, means -for magnetically re
cording more than one conversation on the trans
mitting track of each disc, means for transmit
ting all the recorded conversations over said
60 trunk line at a higher; speed than that at which
lines ' are simultaneously recorded and repro
duced and transmitted over the trunk line, said
disc having another sound track, concentric with
the ?rst, and means for recording all voice cur
rents received from'the trunk line, on said last
soundtrack and reproducing and distributing
them to the various’ lines.
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